[teryn]

Non-airfoiled surfaces (flat plates) create more drag than airfoiled surfaces; airfoils do not necessarily create more lift (or, in this case, lateral-directional stability) compared with flat plates. So it really comes down a drag issue.

Below 10 deg, the variation of lift coefficient with alpha (lift-curve slope) for a flat plate is 2*pi (for alphas < ~11 deg). Most airfoils used for subsonic aircraft have lift-curve slope values very, very close to this. This means that a flat plate is as effective at producing lift as a typical airfoil. It just produces a lot more drag for the same lift.